The present invention generally relates to a bi-stable valve especially useful for pressurizing pen refills. More specifically, the present invention relates to a normally open valve having a bi-stable element, wherein a sudden loss of pressure from one port causes the valve to close, generally irreversibly.
Writing instruments such as pens are commonly provided with a cartridge or a refill such that, when the ink within the pen or refill is fully depleted, only the refill requires replacement. As a result, a variety of decorative pen housings can be provided to receive a standard refill so that the housing can be used repeatedly, requiring replacement of the refill only.
Refills may be pressurized, whereby a smooth and continuous flow of ink is produced regardless of the orientation of the pen itself. For a disposable product, it is preferable that the refill be supplied to the end user pressurized, without subsequent repressurization being necessary.
Pressurization may be achieved by providing chemicals within the refill that react over time, creating gas reaction products that maintain the pressure of the sealed refill tube. This is relatively complicated, expensive and imprecise.
Another method of pressurizing a refill involves pushing a stopper into the open proximal end of the ink tube, whereby the air between the end of the ink column and the stopper is compressed. With this method, the amount of ink that may be loaded into the ink tube is limited, because a portion of the volume, which is needed to compress the column of air, is lost as storage space for the ink.
Yet another method of introducing gas into a refill employs a valve pressed into the proximal end of the ink tube. For example, in the minimal configuration the valve employs one seal (U.S. Pat. No. 4,587,999, to Boiko, et al.), or three or more in a more complex configuration (U.S. Pat. No. 5,738,459 to Smith). Such valves necessarily must have low sealing forces, as the small size of the valve limits the size of springs or other elements employed to close the valve. Imperfections or contaminants on the sealing surfaces may thereby result in loss of pressurization.
A need, therefore, exists for an inexpensive and reliable valve capable of generating high sealing forces that also provides for self-actuated closure.
The present invention provides an initially open valve assembly having an inlet (proximal end) and an outlet (distal end) and a bi-stable element therebetween that closes the valve upon sudden reduction of inlet pressure. In a preferred embodiment, the valve assembly is used in a pen refill.
The bi-stable element has an open mode, whereby fluid, particularly gaseous fluid is allowed to flow therethrough, and a closed mode wherein fluid flow therethrough is blocked. The bi-stable element is preferably a curved disk molded in the closed mode shape from an elastomeric or polymeric material. The valve assembly may be pressed into the proximal end of the tubular ink reservoir of a refill, with the valve in the initially open mode. Once the reservoir is pressurized, inlet pressure may be rapidly reduced, causing the disk to become unstable and invert. The force generated by the inversion of the disk is used to assist the closure of the valve.
The valve assembly comprises at least one distal port and at least one proximal port. An inner support serves to enhance the sealing of an annular ring seal against the inner surface of ink reservoir, to carry the at least one proximal (inlet) port, and, optionally, a sealing plug or other element for sealing the at least one distal port. The bi-stable element comprises means for closing the valve, and generally also comprises at least one distal (outlet) port for allowing fluid passage into the body of the refill. The bi-stable element preferably comprises a curved disk, which may have varying thickness, and which may optionally have a thickened central area (boss) for enhancing the sealing of a proximal port penetrating the disk at that point. The disk may optionally carry a plug or other means for sealing the proximal port. The periphery of the disk, forming a continuous seal to the annular ring, is preferably reduced in thickness to allow for inversion of the disk. It is preferred that, given a flow rate, the pressure drop across the proximal port is greater than that across the distal port, so that the bi-stable element may be quickly actuated with minimal loss of refill pressure.
It is an object of the present invention, therefore, to provide a bi-stable valve element.
It is another object of the invention to provide a bi-stable valve for pen refills, whereby the valve is automatically closed upon the release of inlet pressure.
It is another object of one embodiment of the invention to provide an irreversible valve closure.
It is another object of one embodiment of the invention to provide visual indication of valve closure in a valve having a bi-stable element.
It is another object of the invention to provide a curved disk for use as a bi-stable element in a valve.